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Chemical Composition of the Walls of Certain Algae.*

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Chemical Composition of the Walls of Certain Algae.* CHEMICAL COMPOSITION OF THE WALLS OF CERTAIN ALGAE.* MARY E. WURDACK Ohio State University INTRODUCTION. In spite of the fact that numerous investigations of the nature of cell walls of algae have been made, the recorded data are still far too incomplete to be of the greatest service to science. It is usually impossible to obtain from the literature a complete record of the composition of the walls of the most commonly occurring fresh water algae. The physiological nature of the cell walls of algae appears to play an important role in such phenomena as the resistance of certain algae to desiccation during dry seasons, the rate of entrance of certain mineral elements, the attachment or nonattachment of epiphytic algae, and the utilization of algae as food by fishes and other aquatic animals. It seems important that a thorough knowledge of the composition of the cell walls of algae should be obtained. The object of the investigation reported below was to determine the composition of the cell walls of some of our common algae. Representatives of the following genera were studied: Vaucheria, Cladophora, Oedogonium, Spirogyra, Zygnema, and Draparnaldia, LITERATURE. Only those papers dealing with investigation of the genera listed above will be reviewed in this paper. In 1913, Mirande (4) reported that the cell walls of Vaucheria were composed entirely of cellulose-pectic compounds. He did not state whether these compounds were intermingled or in separate layers, or in what form the pectic compounds occurred.. Brand (1) states that stratification of the cell walls of Cladophora glomerata begins in a very early stage, young fil^ arnents of two cells being composed of two layers. The outer- most layer surrounds the entire filament and is loosened from *Papers from the Department of Botany, Ohio State University,. No. 141. 181 182 MARY E. WURDACK Vol. XXIII it by dilute acetic acid or other weak acids. Potassium hydrox- ide, alcohol, and acid free glycerine have no effect on it. This membrane appears to be independent of either of the other two membranes constituting the second layer of the cell wall. It gave no positive reactions for cellulose. The cellulose reac- tion was obtained with difficulty, so that it seemed that the pectic compounds predominated in the membrane. Chlorzinc iodide gave no blue color even after boiling with hydrochloric acid. Him (3) found the cell walls of Oedogonium to be composed of two layers. The inner one was a moderately thick layer of cellulose and the other a "cuticle" which enclosed the entire filament. This "cuticle" could not be identified with that of the higher plants by means of either stains or other reagents. Him also reports (3) that the beginning of the new partition wall in Oedogonium was at first a thin cellulose ring. This ring enlarges and appears stratified, and separates into two entirely different regions. The outer one of these regions gives a pos- itive cellulose reaction and the inner one a negative reaction for cellulose. Klebahn says [according to West (7) and Olt- manns (6)] that the ring is of a gelatinous nature and stains with haematoxylin. The young membrane which comes from the ring stains in the same manner while the older membranes do not. Czapek (2), in his discussion of the cell walls of the green algae, states that Klebs found the wall inside the gelatinous sheath of Zygnema sp. to have no homogeneous composition. Part of the membrane, which in the normal cell membrane stained with the aniline dyes, was dissolved by heating in dilute hydrochloric acid. The remainder of the cell wall was readily dissolved in copperoxide ammonia, stained with congo red and gave the usual cellulose reactions. West (7) reports all the members of the group Conjugate to have a firm cellulose wall and some to have a great develop- ment of the mucilaginous pectose constituents of the cell wall. This development may be through the conversion of the outer cellulose layers into mucilage or by mucilage being contin- ually exuded through the cell wall. NO. 4 CHEMICAL COMPOSITION OF CERTAIN ALGAE 183 METHODS OF INVESTIGATION. All the filaments were mounted in distilled water and examined in polarized light. The results of these data were then checked by color reactions, hydrolysis, and solubility of the membranes. The -following tests were used in the identification of the substances found: 1. Cellulose. Cellulose is doubly refractive in polarized light, stains blue with iodine potassium iodide and 70% sul- phuric acid, and is soluble in copperoxide ammonia. The filaments are left intact when the cellulose has been removed and will then give a negative hydrocellulose reaction and show no double refraction in polarized light. 2. Pectic Compounds. All pectic compounds are singly refractive in polarized light. The different compounds are dis- tinguished by their different solubilities. Pectic acid is soluble in 2% potassium hydroxide or in 5% sodium carbonate, and is dissolved from the filament by treating it with either of these reagents. If the filament still shows the presence of a pectic compound it is then treated for the removal of calcium pectate. Calcium pectate is broken down by 2% oxalic acid, giving calcium oxalate crystals and pectic acid. The calcium oxalate crystals may be recognized by their tetragonal shape and their double refraction of polarized light. The pectic acid may be removed by dissolving it in 2% potassium hydroxide or 5% sodium carbonate as stated above. Any pectic compound remaining is pectose and is dissolved by heating the filament on the water bath 20—30 minutes in 2% hydrochloric acid and then treating with 2% potassium hydroxide. The hydrochloric acid breaks the pectose down to pectin or pectic acid. If to pectin, the compound is removed by washing the filament in water. If to pectic acid the potas- sium hydroxide dissolves it. If fresh untreated tissue is used in making these tests, the cells are left intact after all the pectic compounds have been removed. These cell walls will then react negatively for pectic compounds in polarized light, but positive by for any other substance composing the walls. 3. Chitin. Chitin, when present, seems to be in a thin layer on the outside. It is singly refractive and can not be distin- 184 MARY E. WURDACK Vol. XXIII guished from the pectic compounds in polarized light. Tissues containing chitin give a positive chitosan reaction. Filaments of the alga are placed in boiling concentrated (50%) potassium hydroxide, and allowed to boil in a covered dish for 30 minutes. The filaments are then hardened in 90% alcohol, mounted in iodine potassium iodide, and dilute sulphuric acid added. A red violet color, characteristic of chitosan, is obtained. REPORT OF INVESTIGATION. VAUCHERIA GEMINATA. In polarized light the cell walls of Vaucheria geminata axe composed of two layers, the outer one being singly refractive and the inner one doubly refractive. This outer layer gives positive reaction to all tests for pectose. Other pectic compounds, if present, occur only in small amounts. Before treating with the pectose solvents the inner layer reacts negatively to the hydrocellulose reaction, although it is dis- solved in copper oxide ammonia if left in the solution two days, the solution being changed three times. After the removal of the cellulose the filament, now composed only of pectose walls, is left intact although very fragile. After removing the outer layer of pectic compounds, the inner layer of the cell wall reacts readily to the cellulose reagents, giving a positive test to the hydrocellulose reaction and dissolving rapidly on the slide in copperoxide ammonia. The entire cell wall is dissolved when treated with the solvents for both pectic compounds and cellulose. The mature oospore seems to have a layer in addition to the two present in the cells of the filament. A thin membrane is left intact after both the pectic compounds and the cellulose have been removed. This membrane is broken by the pressure of the cell contents while the swelling cellulose is being dis- solved. The cell contents move out of the oospore wall leaving it intact as an empty shell. This shell is singly refractive. It may be chitin but the exact composition has not been determined. To summarize the work on Vaucheria geminata: the cell walls are composed of pectose and cellulose, the former being on the outside. This outer pectic layer is very difficultly permeable to cellulose reagents, particularly those used in the hydrocel- lulose reaction, presumably iodine, though this point was not No, 4 CHEMICAL COMPOSITION OF CERTAIN ALGAE 185 definitely determined. The mature oospore has an additional outer layer which may be chitin. CLADOPHORA GLOMERATA. The cell walls of Cladophora glomerata are composed of three layers. The outermost layer is of chitin and can be separated from the rest of the filament by dilute acetic acid. This layer is singly refractive in polarized light, insoluble in either pectic or cellulose solvents, and gives a positive chitosan reaction. The second layer is also singly refractive in polarized light but is soluble in the pectose solvents. The inner layer is doubly refractive in polarized light but gives the characteristic cellulose reactions only after the filament has been treated with pectose solvents. Then the cellulose is readily dissolved leaving only the outermost layer of chitin. Therefore, the cell walls of Cladophora glomerata are com- posed of three layers: chitin, pectose, and cellulose. The layer of chitin is readily separated from the rest of the cell wall and is the only membrane left intact after the filaments have been treated with pectose and cellulose solvents. This layer is also evidently very difficultly permeable to cellulose reagents until partially hydrolyzed.
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